Light-sensitive photographic element and process using it



Sept. 2, 1952 c. WALLER ET AL 2,609,292

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.Harold wezz ic'iIlSolz @Y m@ www Patented Sept. 2, 1952 LIGHT-SENSITIVEPHOTOGRAPHIC ELE- MENT AND PROCESS USING IT Cecil Wallerand Harold OwenDickinson, Ilford, England, assignors to Ilford Limited, Ilford,England, a British company Application July 9, 1946, Serial No. 682,300In Great Britain July 10, 1945 This invention relates to the productionof coloured colloid layers and more particularly to the production ofmultilayer materials for colour photography and to the processing ofsuch may terials.

the colloid layer becomes coloured to a yellow to' red or brown hue.

More particularly according to the invention the substantiallycolourless colloid layer containing silver sulphide nuclei also containsa silver compound as a source of silver ions, or is coated adjacent to asecond colloid layer which contains a silver compound as a source ofsilver ions, and the treatment with the reducing agent is effected inthe presence of a solvent for the silver compound, e. g. sodiumthiosulphate or thiocyanate.

' A useful way of forming the coloured colloid layer is to coat insuper-position on a support a colloid layer containing silver sulphidenuclei and a colloid layer containing silver halide, and to treat thecombination with a reducing agent, e. g. a photographic developer,containing a silver halide solvent.

Alternatively a proportion of silver halide may be included in thecolloid layer containing the silver sulphide nuclei and the layertreated with a photographic developer containing a Vsilver halidesolvent.

Colloid layers containing silver sulphide nuclei may be prepared byvarious methods. When the colloid is gelatin the mere addition of silvernitrate followed by a short heating, e. g. at 120 F., may be suflicientto cause formation of suilicient silver sulphide nuclei by reactionbetween the silver nitrate and the sulphur compounds naturally presentin gelatin. Alternatively, instead of using silver nitrate or othersoluble silver salt, a small quantity of a silver halide, preferably inthe form of a photographic emulsion, may be employed. When using gelatincontaining little or no sulphur compounds, or when using other colloidsfree from sulphur compounds, it is necessary to add to the colloid aquantity of a sulphur 87Claims. (Cl. 95-2) compound which will reactwith the silver nitrate or silver halide to form suflicient silversulphide. Suitable sulphur compounds which may be thus employed arethiourea, allyl thiourea, thiosulphates, thiosemicarbazide and allylthiosemicarbazide. Generally speaking, for a gelatin containing littleor no sulphur compounds (a so-called inert gelatin) quantities of theorder of 5 cc.r of M/lOO silver nitrate and 2.5 cc. of M/ thiourea per100 cc. of a 5% solution of the gelatin are found to be suitable,

The formation of the silver sulphide nuclei is best eiected by heatingthe gelatin containing the silver compound and the sulphur compound fora short period. Temperatures of the order of F. are Vsuitable and theduration of the heating may be from 5 to 60 minutes or more, though theshorterfperiods of treating are usually adequate. It is perferable thatthe pH of the solution should be above about 5.8.

Colloid layers thus prepared are substantially colourless .since thesilver sulphide nuclei impart no appreciable colour or opacity to thecolloid` As already indicated, the coloured colloid layers .of thisinvention are of particular value as lter-A layers inmultilayerphotographic elements for usev in .colour photography, and according toa further feature of this invention, therefore, a photographic elementcomprising a plurality of photographic emulsion layers carried on asupport also includes a layer or layers of a substantially colourlesscolloid containing silver sulphide nuclei, such layer or layerscontaining a silver compound as a source of silver ions or being coatedadjacent to a silver halide emulsion layer.

When such a photographic element is developed with a photographiedeveloper containing a silver halide solvent, the said colloid layercontaining silver sulphide nuclei is developed to a yellow-to red orbrown hue.

In particular, according to this invention, there is provided aphotographic element which comprises the following layers:

(a) A transparent, substantially colourless support.

(b) A silver'halide emulsion layer sensitive to red light.

(c) A layerl of colourless colloid containing silver sulphide nucleiwhich, on development with and an outer colioid layer toactasan'anti-abrasion layer or ultra-violet ray absorbing layer. f

Such a photographic element, exposed to record v a coloured object, therays 'beingjncident on layer emulsion layers.

vOn treating the iinal product with Farmers reducer all the silver andsilver salts are removed, and the colour of layers c and e is alsoremoved, leaving a true colour record of the originalobiect.

Many variations may be made in this procedure Without departing from theessential features of this invention. For example the layers b and d maybe transposed and their processing correspondingly varied.. lFurther thelayers c :and-fe may be adapted "to yield `rector".red-brown images andthe `colour of the exposing "light used Y for re-exposing the layerscorrespondingly adjusted to a wavelength, or band of wavelengths,

-. :which .areabsorbed by such layers c and c. V1t .fis sometimesconsidered desirable when using a photographic element of the generalcharacter' referred'to above to remove the firstgraphic developer, theseare converted to silver image colour separation negative records andthefugitive dyestui is removed. If the photographic Adeveloper contains asilver solvent, or if the elel- Vineni'gis subsequently treated witha'photographic developer containing a silver solvent, layersV yc and ebecome coloured.V The fugitive dyestuf in layer e 'may be replaced bycolloidal silver which im partsa yellow colour'to the layer. y

` The intensity of the developed colour depends `ontheparticularfconditions prevailing, i. e. on

:the nature-of the layers cand ve and on the development conditions. A-veryv intense colouration is'usually obtained by including a/source ofsilver ions in the layers c and 'e themselvesfor example by including' asmallproportion of silver halide.Y lnv order to keep-the 4transparencyof such layers,v before vdevelopment to colour, as high-asy possible,the added silver halide can usefully be a line grain emulsionsincethisisnot only of high transparency but, presumably by vreason of vtheliinenerss of grain of the silver halide, is very reactiveas a'source ofsilver ions. The nature and quantity of the silver halide added' shouldnot be suclnho'wever, that any substantial 'light-sensitivity-'isimparted to layers c ande since these should not give any Vappreciableblack silver image on development.

The `emulsion layers of the photographic ele- 'ment :obtained by theprocedure outlined above can be :further selectively processed to colourby making use of the coloured layers c and e Yas light-barrier layers.For example the element may be exposed to blue light through the supportand then developed in a solution containing :an aromatic Yprimary .aminodeveloping agent and a colourl-former .which combines With the oxidation.products of such developing agent, formed during development, to form abluegreen azomethineor quinone-imine dyeimage in situ with the developedpositive record in layer b. The .element `may then beexposed to blue'lightincident on layer f and that layer similarly processed `to 'form apositive yellow image in layer j. Neither of these treatments affectlayer d since the blue exposing light is absorbed by the yellow layers cand e. Layer d may then be rendered developable either by exposure tovery bright light, Yadequate to penetrate 'layer c or e or by X-rays orby chemical treatment, e. g. With a 5% aqueous solution of sodiumarsenite or hydrogen peroxide or with guanidine thiocyanate. This layer.may .be similarly developed to form in it a positive magenta image.

g halide records developable.

formed;1neg'ative" .silver records before re-exposing'to'render thecomplementary positive silver With the types of light-barrier layerwhich have been prepared in the past, e. g. dyestuis or black metallicsilver layers (formed from .pre-fogged silver halide layers as describedA'in British Patent No. 505,099), the removal of the negative *silverimages has 'been impractical-ble since the treatment, usually With aciddichromate or acidpermanganate, has also removed theY dyestuis ormetallic silver from the barrier layer.

`It `has lbeen found, however, that with fthe light-barrier Vlayers ofthe present vinvention the removalof the original negative silver imagebefore exposure is `possible since the silver sulphide nuclei are.substantially unaffected bythe usual aciddichromate :bleach 'baths anda re-develop- Ament of the element with a developer containing a silverhalide solvent results in colouration of the layers. V ,Accordingly an"important eature of the pres- .ent .invention consists inthe processingof an element of the general character of that set out above by thefollowing steps:

:1. 'Develop to form original negative in'l'ayersb; d and T2. .Bleach`out the records 'formed in 1 by an acid dichroinate lbleach bath'. Atthis stage the dye in layer e has been bleached out by `the treatments.specied and if colloidal silver is used instead of dye'this lalso isremoved.

3. 'Develop in 'a :developer containing a silver halide solvent. y 4.Ete-expose through'the' support a with light absorbed Aby the layer cand colour develop to form a positive blue-green azomethine orquinone-imine dyeiniagein b.

Syrie-expose with light falling on Ilayer `j and absorbed by layer e andcolourdevelop to'form a positive yellow azomethine' or quinone-imine dyeimage in j.

i6. Treat' the assembly to render the silver halide in Alayerdevelopable and colour develop to form a positive magenta azomethine orquirione-"iminedye imagein d.

7. Remove silver, silver salts and the colour in layers -c and 'e withFarmers reducer.

Appropriate variations would be made in this process lwere the layers band d reversed. The following example will vserve toillustrate theproduction -rof la coloured colloidA layer and of a photographic'element and its processing, according tothe invention.

y y Example Y V16k-photographic multi-layer element was preparedconsisting of the `following layers in superposition inthe order stated.l

(a) Transparent colourless fllmsupport.

' (b) Gelatino silver iodobromide emulsion, sensitised to thered'reg'ion of the spectrum by means of 2.2'.8triethyl4.4'dichloroethiacarbocyanine bromide. (c) Gelatin layer containing rsilver`sulphide nuclei'and silver halide (prepared as described below). L

(d) Gelatine silver iodobromide emulsion, sensitised to the green regionof the spectrum by means of 2.2'-diethyl-pseudocyanine iodide.

(e) Gelatin layer containing silver sulphide nuclei and silver halide(prepared asdescribed below)- and containing the dyestul-pf-sulphophenyl-S-methyl Vl 'cinnamylidene-pyrazoleone. A y v (f)Gelatino silver iodobromide emulsion having anatural sensitivity intheblue region of the spectrum and substantially insensitive to the greenand red regions of the spectrum.. -l The layers c and e were prepared byadding to a 5% solution of gelatin, 5 cc. of AM/100fsilver nitratesolution and 2.5 cc. of` M/100l thiourea solution per 100 cc. of gelatinsolution, digesting at 120 F. for 60 minutes, and adding 10 cc. of finegrain silver iodobromide emulsion (containing 250 mgm. of silver) per100 cc. of gelatin soluf tion. In the case of layer ea quantity of thestated dye equal to 5% on the weight of the gelatin was addedy y 'Iheelement thus prepared was exposed to` a coloured object, the light beingincident on layer f and developed for 3 minutes in a metol-hy- Water andre-developed for 8 minutesintafdeveloper consisting of:

An1id0'l V f 7.5 Sodium sulphite (anhyd.) 30 Sodium carbonate (anhyd.)y.40 Potassium thiocyanate 1;.0 Potassium'bromide i `1`.0

Water up to 1000 cc.

At this stage the `originally developed silver images `had been removed(by the dichromate bath), the dye in layer e had been removed (on theoriginal development) anda yellow-red colour had been formed in layers cand e (by the amidol development).

The element was then exposed toviolet light passing through the supporta and then developed in a developer of the following composition:

N.Ndiethy1 p-phenyiene diamine hydrochloride gm 0.4 Ethyl alcohol cc 40Sodium carbonate (Na2CO3.10I-I2O) 20%A` solution cc 160 Sodium sulphite(NazSOs.7H2O) r20% solution Cc 25 2.4-dichlor-a-naphtho1 gm 0.4Potassium bromide gm' 0 .1

Water to make 400 cc.`

This treatment resulted in the formation of a positive silver plusvblue-green indophenol dye image in layer b. The element was then re- 62washed andV exposed ltof=violetl lightfalling-'on layer f. It'was thenredeveloped in afdeveloper of "the: formula vgiven above' butcontaining'2+ chloracetoacetanilide "(0.4 gm.) instead of4 2.4-dichlorea-naphthol. By. this means a positive silver plusl yellowvazomethine dye image was formedin layer f.y -t j A n n The element waslthen-re-.washed andv exposed to X-rays, rendering f, thefresidualsilver rhalide inlayer d developable.' It was then developed in adeveloper as above but containing iep-nitro.-l phenyl-3-methyl5epyrazolone (0.4 gm.) :instead of the 2.4-dichlor-a-naphthol. Thisresulted in the formation of a positive silver plus magenta yazomethinedye image in layer d.

The element Was'then re-Washed and bathed in Farmers reducer, vwhichremoved all the silver and silver salts and also the colour from layersc and e, leaving a fullcolour image of the original object. The linegrain emulsionincluded in layersc and e' was too slow to record; an'imagejduring the various exposure operations. j

The process described above and'exemplied in the foregoing example maybe modiiied'in various ways. For example, the-'exposedV positive silverhalide records may be processed to colour by methods other thancolour-development, e. g. by dye toning or chemical toning. f

'Moreover, one or more'ofthe emulsion layers may contain colour-immers;-the following isan example of such a process: 4

Example A photographic multi-layer element wasf'prepared consisting ofthe following layers in superposition in the order stated as illustratedin the accompanying drawing:

(a) Transparent colourless lm support.V '(b) Gelatino silver iodobromide'emulsionsenf sitised to the red region by means of2:2"8-'triethyl-4*:4dichlorwo thiacarbocyanine bromide and containing 2parts v`olfl-hydroxy-Z-naphthoyl stearylamide-lfsulphonic acid yper`parts of emulsion. A I Y (c) Gelatin layer containing silver sulphidenuclei and silverhalide (prepared as'described below). f

(d) Gelatino silver iodobromide emulsion, sensitised to the green regionf -the spectrum by means of 2.2f-diethyl-pseudocyanineiodide.V

(e) Gelatin layer containing silver sulphide nuclei and silver halideand yellow colloidal Esilver as lter medium. Thelatter isprepared by thereduction of an aqueous solution of silver nitrate in thepresence ofgelatin by glycine. l (f) Gelatino silver iodobromide emulsionihaving anatural sensitivity in the blue region of the spectrum andsubstantiallyl -insensitive to th green and red regions of the spectrum.I The layers c ande were preparedas for the previous example. A r n Theelement thus prepared was exposed to a coloured object, the light beingincident Aon layer f. It was then developed .for-B'minutes', in

a developer of the following formula:

Gms. Metol Q 3 Sodium sulphite (anhydrous) Hydroquinone 16V Sodiumcarbonate (anhydrous) 37.5 Sodium thiocyanate '2 Eotassium bromide 2Water to 1 litre.

This produced negative yrecords in -silver in layersb.. d andicorresponding to the blue, green and red aspects of'the object-and, inaddition, produceda uniform yellow-brown silver deposit in. layers cande. The element was then washed in -runningfwater for 20 minutesyielding the product identified as stage l in the accompany,- ingdrawing, and then processed Vto givef afull colour image in thefollowing stages: i

. 1. Exposed to the top layer JJt'o .blue light, the exposure beingconfined to this layer by the barrierilayer e. s f

2. This layer colour-developed'4 in `a yellow colour developer ofthefollowing composition:

N.Ndiethyl p-phenylene diamine hydro- Water to make 400 cc..

3. Washed for l minutes. The element was then at stage 2 shown in thedrawing.

4. rThe bottom layer b exposed to blue light, exposure being confined tothis layer by means of the barrier layer c.

5. "Colour-developed in a developer of the following composition:

mN-diethyi p-phenylene diamine hydrochloride gm 0.4 Ethyl alcohol cc 40Sodium carbonate (NazCO3-l0I-I2O) 20% solution cc 160 Sodium sulphite(NazSO3-7H2O) 20% soluy tion cc 25 Potassium bromide gm-- 0.1

Water-5to make 10D-cc.

6. Washed for l0 minutes.' Theelement lwas then at stage 3 shown in thedrawing.

7. The middle layer d exposedirom both sides to white light. White lightwill penetrate' the barrier layers. "'v Y y `8. This layercolour-developed in a magenta colour developer of the followingcomposition:

chloride ',i g m. 0.4 Ethyl alcohol cc 40 Sodium carbonate(NazCOalO'I-IzO) 20% solution f cc 160 Sodium sulphite (Na2SOs-7HzO).20% solution i cc l-p nitrophenyl 3 methyl 5 pyrazo- Alone gm 0.8

9. Washed for minutes. The element was then at stage 4 shownin thedrawing. y

10. 'Fixed and bleached in Farmers reducer.

1l. Washed for 20 minutes. `The elementwas then at 'stage 5 shown in thedrawing. The full colour image of the originalobjectwas therebyobtained.

What we claim is: K

,1. A photographic element which comprises a support Vcarrying at leastthree superimposed layers, the outer ones of which are colloid silverhalide photographic emulsion layers and the middle one of which is alayer of substantially colourless colloid containing silver sluphidenuclei, of such particle size and quantity that they impart no colour tothe layer, the said colourless colloid' containing a quantity of silvercompound insuiliciently sensitive to light Vto produce any appreciableimage in the-saidcolourless colloid layer on photographic development,but suiiicient in quantity to producegwith'thei aid 'of said silversulphide nuclei, alayer of silversubstantially opaque to blue light onphotographic development.

2. A photographic element which comprises v(a) a transparentVsubstantially colourless sup-- port and in superimposition thereon, inorder, (b) asilver halide emulsion layer sensitive to red light, (c) alayer ofA a colourless colloid containing silver sulphide nuclei ofsuchparticle size and quantity that they 'impart no colourl to thelayer, and a quantity 'of a silver compound soluble in alkalithiosulphate insufficiently sensitive to light to yield any appreciableimage on photographic development but suiiicient in quantity to produce,with the aid of said silver sulphide nuclei,'a4 layer of silver`substantially opaque to blue light on photographic'develop* ment (d) asilver halide emulsion layer sensitive to green light, (e) a layer ofcolourless colloid containing silver sulphide nuclei of such particlesize and quantity that they impart nocolou'rrto the layer, and aquantity of a silver compound soluble in alkali thiosulphateinsufficiently sensitive to light to yield any appreciable image onphotographic development but suiiicient in quantity to produce, with theaid of said silver sulphide nuclei, a layer of silver substantiallyopaque to blue light on photographic development, and a removable yellowcolouring material, and (f) a silver halide emulsion sensitive only tobluelight.

`3. A photographic element which comprises (a) a transparentsubstantially colourless support and in superimposition thereon, inorder, (b) a silver halide emulsion layer sensitive'to red light, (c) alayer of a colourless colloid containing silver sulphide nuclei of suchparticle size and quantity that they impart `no colour` to the layer,and a quantity of silver rhalide insuf'- flciently sensitive to lighttofyield any` appreciable l, image on photographic development butsuflicient in quantity to produce, with the aid of said silver sulphidenuclei, a layer of. silver.` substantially opaque to blue light onphotographic development, (d) a silver halide emulsionlayer sensitive togreen light, (e) a layer of colourless Acolloid containingsilversulphide nuclei of such'lpfflrticle size and quantity that theyimpart no colour to the layer, and a quantity of silver halideinsufently sensitive to light to Vyield any appreciable image onphotographic development but Asuicient in quantity to produce, withtheaid of said silver sulphide nuclei, a layer of 'silvensubsta'ntiallyopaque to blue lighten photographic development, and a removable yellowcolouring'material, and (f) a silver halide emulsion' sensitive only toblue light.

4. A photographic element which comprises (a) a transparentsubstantially colourless support and in superimposition thereon,.inorder, (b) a silver halide emulsion layer sensitive to red light, (c) alayer of a colourless colloid containing silver sulphide nuclei of suchparticle size and quantity that they impart no colour to the layenand aquantity of an emulsion of silver halide insufficiently sensitive tolight to yield any appreciable image on photographic development butsufcient in quantity to produce, with the aid of said silver sulphidenuclei, a layer of silver substantially opaque to blue light onphotographic development, (d) a silver halide emullof'sanv emulsion, of.silver` halide insuiiiciently sensitive to light to ,yieldany1;altlpreciable` image en .photographic development but suicient in.quantity to,.produce, withthe.aid of said's'ilver sulphide :nuclei, alayer of lsilver substantially opaque. toblue light on photographic`development, and-fa removable yellow colouring material, and (f)afsilver halide emulsionsensitiveponly to blue light.

5. A photographic element which comprises (a) Aa'transparentsubstantially colourless support and' in superimposition thereon, inorder, 1(1))A a silverhalide emulsion layersensitive to red light,` (c)a layer of a colourless colloid containing silver sulphide nuclei ofsuch particle size and quantity that they impart no colour to the layer,and a quantity of an emulsion of silver halide insuiiiciently sensitiveto light to yield any appreciable image on photographic development butsulcient in quantity to produce, with the aid of said silver sulphidenuclei, a layer of silver substantially opaque to blue light onphotographic development, (d) a silver halide emulsion layer sensitiveto green light, (e) a layer of colourless colloid containing silversulphide nuclei of such particle size and quantity that they impart nocolour to the layer, and a quantity of an emulsion of silver halideinsuiciently sensitive to light to yield any appreciable image onphotographic development but sufficient in quantity to produce, with theaid of said silver sulphide nuclei, a layer of silver substantiallyopaque to blue light on photographic development, and yellow colloidalsilver, and (f) a silver halide emulsion sensitive only to blue light.

6. A process of colour photography which includes the step of treatingan exposed photographic element which comprises (a) a transparentsubstantially colourless support and in super-imposition thereon, inorder, (b) a silver halide emulsion layer sensitive to red light, (c) alayer of a colourless colloid containing silver sulphide nuclei of suchparticle size and quantity that they impart no colour to the layer and aquantity of a silver compound soluble in alkali thiosulphateinsufficiently sensitive to light to yield any appreciable image onphotographic development but sufficient in quantity to produce, with theaid of said silver sulphide nuclei, a layer of silver substantiallyopaque to lblue light on photographic development, (d) a silver halideemulsion layer sensitive to green light, (e) a layer of colourlesscolloid containing silver sulphide nuclei of such particle size andquantity that they impart no colour to the layer and a quantity of asilver compound soluble in alkali thiosulphate insufficiently sensitiveto light to yield any appreciable image on photographic development butsuicient in quantity to produce, with the aid of said silver sulphidenuclei, a layer of silver substantially opaque to blue light onphotographic development, and a removable yellow colouring material, and(f) a silver halide emulsion sensitive only to blue light with aphotographic developer containing a solvent for silver halide.

7. A process of colour photography which comprises treating an exposedphotographic element which comprises (a) .a transparent substantiallycolourless support and in superimposition thereon, in order, (b) asilver halide emul- 10 sion layer sensitive j to redl light;V (c) alayer y.of a colourless :colloid .zcontaining silver.- sulphide nucleiof such particlesize and quantity :that they impartv no. 'colourrtdthe-` layer land; a quantity' of a vsilverlcompound:soluble'.in-.-alkalithiosulphate insuiciently sensitiveto,lightltof yield any appreciable ,i1nage;;l 0.11 photographicdevelopment but sufjcientin ,quantity to produca-.with the aid of saidsilver-sulphi nuclei, a; layerof silver substantiallyopaquetox-'bluelight on photographicdevelopmentgKd), a silver halideemulsion layer sensitive to green light, (e) a layer of colourlesscolloidl. containing silver sulphide nuclei of such particle size andquantity that. they impart no colour to the layer anda quantity of asilver compound soluble in alkali- 'thiosulphate insuiciently sensitivetoy light to yield any appreciable image on photographic development.but suilicient in quantity to; produce, with the aid of said silversulphide nuclei, a layer of silver substantially opaque to blue light onphotographic development, and a removable yellow colouring material, and(f) a silver halide emulsion sensitive only to blue light by thefollowing operations: develop in a non-colour-forming developercontaining a solvent for silver halide, expose layer b to blue lightpassing through layer a and re-develop layer b in an aromatic primaryamino colour-developing solution containing a blue-green colour-former,expose layer f to blue light incident on that layer and re-develop layerf in an aromatic primary amino colour-developing solution containing ayellow colour-former, render layer d re-developable and re-develop in anaromatic primary amino colour-developing solution containingA a magentacolour-former, and treat the final product with Farmers reducer toremove all silver and silver salts and all colouration from layers c ande.

8. A process of colour photography which comprises treating an exposedphotographic element which comprises (a) a transparent substantiallycolourless support and in superimposition thereon. in order, (b) asilver halide emulsion layer sensitive to red light, (c) a layer of acolourless colloid layer containing silver sulphide nuclei of suchparticle size and quantity that they impart no colourv to the layer anda quantity of a silver compound soluble in alkali thiosulphateinsufciently sensitive to light to yield any appreciable image onphotographic development but sufficient in quantity to produce, with theaid of said silver sulphide nuclei, a layer of silver substantiallyopaque to blue light on photographic development. (d) a silver halideemulsion layer sensitive to green light, (e) a layer of colourlesscolloid containing silver sulphide nuclei of such particle size andquantity that they impart no colour to the layer and a quantity of asilver compound soluble in alkali thiosulphate insufficiently sensitiveto light to yield any appreciable image on photographic development butsufficient in quantity to produce, with the aid of said silver sulphidenuclei, a layer of silver substantially opaque to blue light onphotographic development, and a removable yellow colouring material, and(f) a silver halide emulsion sensitive only to blue light by thefollowing operations; develop in a non-colour-forming developer, bleachout the developed records in layers bl, d and f, develop in adevelopercontaining a silver halide solvent. expose layer b to blue light passingthrough layer a and re-develop layer b in an aromatic primary aminocolour-developing solution containing a blue-green colour-former,.expose layer f to blue light 'incident ou that layer Yarid re-developlayer f in an aromatic primary amino colour-developing solutioncontaining a yellow colour-former, render layer d, re-developable andre-develop nlan aromatic primary amino colourdeveloping solutioncontaininga magenta colourformer, and treat the nal product vwithFarmers reducer toremove all silver and silver salts and all colourationfrom layers candf e.

CECIL WALLER.

HAROLD OWENDICKINSON.

REFERENCES CITED The `following references are of record in' the le ofthis patent:

UNITED STATES PATENTS Name Date- Number I5 Number Name Date Wendt 4--Feb. 21, v1933 Knocher July 27, 1937 Eggert et a1. Apr. 11, 1939 SchnzelSept. 5, 1939 Seaseret al Feb. 27, 1940 Sease et al.V Nov. 11, 419,41Schinzel- Sept. 8, 1942 Eggert et a1., June 1,1943 Carroll Aug. 24,19.43 Rott June 20, 1944 Staud May 15, 1945 FOREIGN PATENTS Country DateGreat Britain Aug. 24, 1939 France Dec. 10, `19,42 France Sept. 25, 1944

1. A PHOTOGRAPHIC ELEMENT WHICH COMPRISES A SUPPORT CARRYING AT LEASTTHREE SUPERIMPOSED LAYERS, THE OUTER ONES OF WHICH ARE COLLOID SILVERHALIDE PHOTOGRAPHIC EMULSION LAYERS AND THE MIDDLE ONE OF WHICH IS ALAYER OF SUBSTANTIALLY COLOURLESS COLLOID CONTAINING SILVER SLUPHIDENUCLEI, OF SUCH PARTICLE SIZE AND QUANTITY THAT THEY IMPART NO COLOUR TOTHE LAYER, THE SAID COLOURLESS COLLOID CONTAINING A QUANTITY OF SILVERCOMPOUND INSUFFICIENTLY SENSITIVE TO LIGHT TO PRODUCE ANY APPRECIABLEIMAGE IN THE SAID COLOURLESS COLLOID LAYER ON PHOTOGRAPHIC DEVELOPMENT,BUT SUFFICIENT IN QUANTITY TO PRODUCE, WITH THE AID OF SAID SILVERSULPHIDE NUCLEI, A LAYER SILVER SUB-